Conventionally, a gear crank of the type described above and, as shown in FIG. 5, has a pair of crank arms b and c connected integrally with both axial ends of a crank shaft a so as to form a one-piece crank d. A flange e is provided at an end of one crank arm b at one axial end side of crank shaft a, a chain gear f is fitted onto the end of crank shaft a, and a ball holder g is screwed therewith, the ball holder g and flange e holding therebetween the chain gear f. A ball race i is mounted on one axial end of a bottom bracket h of a bicycle. The one-piece crank d is inserted through bottom bracket h from the other crank arm c and balls k are interposed between the ball holder g and the ball race i, so that crank shaft a is supported at its one axial end rotatably to bottom bracket h, At the other axial ends of bottom bracket h and crank shaft a are provided a ball race l and a ball holder m, and balls n are interposed therebetween, so that crank shaft a is supported at the other axial end thereof rotatably to bottom bracket h. A nut o is screwably tightened to crank shaft a outside ball holder m.
With this construction if a tooth breaks on the chain gear f, it needs to be exchanged, and the nut o, ball holder m and ball race l, must be removed following which the, one-piece crank d is drawn out of bottom bracket h, and thereafter chain gear f is removed from crank shaft a by unscrewing ball holder g. A new chain gear is mounted on crank shaft a and the one-piece crank d is reset to bottom bracket h. This exchange of chain gear f is very troublesome and impracticle for a user.